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. Author manuscript; available in PMC: 2018 Nov 13.
Published in final edited form as: Invert Neurosci. 2018 May 30;18(2):8. doi: 10.1007/s10158-018-0211-9

egl-4 modulates electroconvulsive seizure duration in C. elegans

Monica G Risley 1,2, Stephanie P Kelly 1,2, Justin Minnerly 1,2, Kailiang Jia 1,2, Ken Dawson-Scully 1,2,✉
PMCID: PMC6233307  NIHMSID: NIHMS995205  PMID: 29845318

Abstract

Increased neuronal excitability causes seizures with debilitating symptoms. Effective and noninvasive treatments are limited for easing symptoms, partially due to the complexity of the disorder and lack of knowledge of specific molecular faults. An unexplored, novel target for seizure therapeutics is the cGMP/protein kinase G (PKG) pathway, which targets downstream K+ channels, a mechanism similar to Retigabine, a recently FDA-approved antiepileptic drug. Our results demonstrate that increased PKG activity decreased seizure duration in C. elegans utilizing a recently developed electroconvulsive seizure assay. While the fly is a well-established seizure model, C. elegans are an ideal yet unexploited model which easily uptakes drugs and can be utilized for high-throughput screens. In this study, we show that treating the worms with either a potassium channel opener, Retigabine or published pharmaceuticals that increase PKG activity, significantly reduces seizure recovery times. Our results suggest that PKG signaling modulates downstream K+ channel conductance to control seizure recovery time in C. elegans. Hence, we provide powerful evidence, suggesting that pharmacological manipulation of the PKG signaling cascade may control seizure duration across phyla.

Keywords: C. elegans, Seizure, Epilepsy, Protein kinase G, PKG, Electroconvulsive seizure

Introduction

Epilepsy is a neurological disorder characterized by complex physiological and chemical alterations in neuronal firing that affects 1 in 26 people in the USA (Mary Jane et al. 2012). The deteriorating effects of seizures reduce the quality of life and increase healthcare costs for sufferers (Mary Jane et al. 2012; Guerrini et al. 2013). Although the prevalence of seizures is high among Americans, effective and noninvasive treatments are limited for easing symptoms. Several methods are used to correct this condition; the most common are antiepileptic drug (AED) treatment monotherapies and polytherapies (Kim 2014; Loscher and Schmidt 2011; Szaflarski et al. 2014). While AEDs work sufficiently for some of the population, it is estimated that ~30% of epileptic patients do not respond to current drug therapies (Lee 2014; Brodie et al. 2012). As a result, there is a significant need to a gain better understanding of the cellular and physiological mechanisms that underlie both seizure susceptibility and the response to AED treatment.

Caenorhabditis elegans are a powerful in vivo multicellular human disease model for neurodegenerative research including Parkinson’s and Alzheimer’s diseases, autism spectrum disorders, and learning and memory studies (Levitan et al. 1996; Link et al. 2003; Hamamichi et al. 2008; Calahorro and Ruiz-Rubio 2011; Zhang et al. 2005; Saeki et al. 2001). Several attractive features, including a fully mapped connectome of 302 neurons and approximately 7000 synapses as well as readily available RNAi libraries and genetic tools, make it possible to insert GFP-tagged human transgenes and observe them through the transparent cuticle (White et al. 1986; Chalfie et al. 1994; Timmons et al. 2001). In addition, its small size, relatively inexpensive maintenance and short generation time provide a powerful platform to explore as a human seizure model. The past research in our laboratory has established a behavioral method to induce an electroconvulsive seizure (ES) in adult C. elegans (Risley et al. 2016). With this method, we determined that the behavioral recovery from an ES is partly due to contribution of the major inhibitory neurotransmitter, GABA, in the nervous system.

The nitric oxide (NO)/cGMP/PKG signaling pathway, which targets downstream ion channels, is conserved from C. elegans to humans. A Drosophila melanogaster PKG, encoded by the foraging gene, has two natural allelic variants that have been attributed to many behavioral responses including foraging patterns, egg-laying and neuronal protection during anoxic and hyperthermic stresses (Krzyzanowski et al. 2013). Drugs, along with genetics, have been shown to alter the endogenous activity levels of cellular PKG (Dawson-Scully et al. 2010). The C. elegans ortholog of foraging is egl-4 (Daniels et al. 2000). In worms, this gene is neuronally expressed and has been associated with many parallel characteristics of its fly homolog including food search behaviors, egg-laying, memory association and synaptic transmission (Caplan et al. 2013; Dawson-Scully et al. 2010; Kaun et al. 2007; L’Etoile et al. 2002; Mery et al. 2007; Renger et al. 1999).

With this research, we have successfully demonstrated that behavioral recovery time from an electroconvulsive seizure is reduced when PKG activity is increased both genetically and pharmacologically in an egl-4 LoF mutant C. elegans. Caenorhabditis elegans are an ideal system to explore seizure mechanism and novel therapeutic targets that, importantly, respond to human antiepileptic drugs.

Materials and methods

Strains and genetics

Caenorhabditis elegans were maintained on standard NG agar plates seeded with Escherichia coli. L4 worms were picked and transferred the evening prior to testing and maintained overnight at 25 °C. Caenorhabditis elegans used in these experiments were Bristol N2 strain, the loss-of-function egl-4 (n478) IV strain MT1073 and gain-of-function egl-4 (ad450) IV strain DA521. All C. elegans strains were ordered from the Caenorhabditis Genetics Center.

Caenorhabditis elegans electroconvulsive seizure assay

This procedure was performed as described previously (Risley et al. 2016). In brief, 15 μL of standard M9 salt solution was added to 9 mm long segments of clear plastic tubing (Tygon® microbore tubing). Approximately six 1-day-old adult C. elegans were transferred to plastic tube using a platinum wire pick and allowed to incubate for 30 min (Fig. 1a). For the pharmacological treatments, the drug was dissolved directly into the M9 and the worms were incubated for a total of 30 min. Following incubation, an insulated copper wire was inserted into either end of the plastic tube and attached with alligator clips to a square-pulse generating stimulator (Grass, SD9). A shock was delivered for three seconds (3 s, 47 V, Fig. 1b), and a microscope camera recorded the shock and recovery phases. Recovery was manually scored when each individual animal resumed a wave-like swimming motion. All data were pooled and averaged.

Fig. 1.

Fig. 1

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A schematic that represents the position of the worms before and during an ES. a Approximately six worms are added to a plastic tub plugged on either end with copper wire (represented in black). The worms habituated in the aqueous solution for 30 min before the electric shock. During this time, they display normal thrashing motion. b During the shock, some worms will exhibit unilateral body bends, and some will elongate. This is represented by the various positions of the cartoon worms inside the time. The time to resume normal thrashing is recorded as recovery

Pharmaceutical manipulations

Drugs were dissolved directly into the M9 solution, and 15 μL of the solution was aliquot into the clear plastic tubing. The drugs included: 50 mM 8-bromo-cGMP (increases PKG enzymatic activity), 10 mM Rp-8-bromo-cGMP (decreases PKG enzymatic activity) and 0.5 mM Retigabine (K+ channel agonist) purchased from Sigma-Aldrich (St. Louis, Missouri, USA), and 0.5 mM sildenafil citrate was purchased from Attix Pharmaceuticals (Toronto, Ontario, Canada).

Statistics

Induction of electroconvulsive seizure was conducted for at least nine worms and experiments were repeated at least three times on different days. Data were analyzed using a Kruskal–Wallis one-way ANOVA on ranks followed by a Dunn’s method post hoc multiple comparisons test or an unpaired Student’s t test where indicated in the results. All statistics were performed using SigmaPlot 11.0 (San Jose, California). All bar graphs represent mean ± SEM, and asterisks denote significance between bars were * = P ≤ 0.05.

Results

Using a recently developed electroconvulsive seizure assay, we determined that the NO/cGMP/PKG signaling pathway plays a role in recovery from electroconvulsive seizures in C. elegans. Behavioral recovery, determined by the ability to resume normal locomotion, is reflected by the ability for the CNS to function after an electroconvulsive shock. This seizure phenotype is based on the strength and duration of the electrical current passed through the animal. Briefly, worms were placed inside a clear plastic tube containing M9 saline and drug solution (Fig. 1a). Both ends of the tube were plugged with copper wire and connected to a square-pulse generating stimulator. This method allowed us to assess approximately ten worms per experiment. During the seizure episode, worms immediately display paralysis, immediately followed by convulsions. We define convulsions as repeated unilateral body bends and twitching (Fig. 1b).

Genetic PKG activation reduces seizure duration

The increased duration of the electroconvulsive seizure in worms was directly correlated with the decreased concentration of PKG enzymatic activity. Initially, N2, egl-4 [encodes the worm PKG gene; homologous to the foraging gene in flies (Krzyzanowski et al. 2013; L’Etoile et al. 2002)] loss-of-function (LoF; -PKG) and egl-4 gain-of-function (GoF) were explored to determine if PKG plays a role in seizure recovery. After stimulation (3 s, 47 V), worms resumed normal sinusoidal thrashing locomotion. N2 resumed normal locomotion in approximately 47 ± 6.6 s and egl-4 (n478) LoF recovered in 107 ± 17.8 s (one-way ANOVA on ranks, F(2,55) = 15.906, P < 0.001; Dunn, P < 0.05, Fig. 2). egl-4 (ad450) GoF rescued recovery time to N2 levels of 46 ± 18.2 s (Dunn, P < 0.05, Fig. 2).

Fig. 2.

Fig. 2

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Seizure recovery can be mediated by PKG concentrations in C. elegans. N2 wild-type worms and egl-4 GoF mutants took significantly less time to recover from an electroconvulsive seizure when compared to the worms with decreased levels of PKG. Error bars represent ± SEM and n ≥ 15

Pharmacological PKG modulation alters seizure duration in wild-type

Next, we investigated whether drugs that increase and decrease PKG enzymatic activity in wild-type animals would reflect the results of the genetic manipulations. N2 worms were pretreated with two PKG activators, 50 mM 8-bromo-cGMP and 0.5 mM sildenafil citrate and one PKG inhibitor Rp-8-bromo-cGMP (Fig. 3). When exposed to the PKG inhibitor, N2 worms took an average of 71 ± 12.4 s to recover compared to the control N2 at 52 ± 9.8 s. While this average is trending in the direction we hypothesized, and it is not significant compared to control, it was significantly different from both of the PKG activators, 8-bromo-cGMP and sildenafil citrate (Student’s t test, P < 0.05) which recovered at 38 ± 6.6 and 36 ± 7.2 s, respectively.

Fig. 3.

Fig. 3

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Wild-type worms are treated with PKG activators and inhibitors. Pretreatment of wild-type worms with 10 mM of Rp-8-bromo-cGMP (PKG inhibitor) causes a significantly increased time to recovery compared to the worms that are treated with 50 mM 8-bromo-cGMP and 0.5 mM sildenafil citrate (PKG activators). Error bars represent ± SEM and n ≥ 24

PKG activation reduces recovery time in egl-4 LoF

We explored the idea that PKG activation would rescue the time to recovery of the egl-4 LoF. We pretreated N2, egl-4 LoF and egl-4 GoF worms for 30 min with 50 mM 8-bromo-cGMP (Fig. 4). As anticipated, the egl-4 GoF treated with the PKG activator was not significantly different from the control. However, the LoF worms took significantly less time to recover compared to the control, 74 ± 16.5 s and 134 ± 16.7 s, respectively (Student’s t test, P < 0.05).

Fig. 4.

Fig. 4

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Treatment with a PKG activator, 8-bromo-cGMP. When egl-4 LoF were pretreated with 50 mM 8-bromo-cGMP, they took significantly less time to recover compared to the control. There was no significantly difference between the treatment and control for the wild-type or the egl-4 GoF. Error bars represent ± SEM and n ≥ 9

Antiepileptic drug reduces seizure duration in egl-4

Previous investigations from our laboratory have determined that C. elegans susceptible to seizures respond to human AEDs; therefore, we wanted to test if the PKG mutant could also be rescued with an AED. N2 and egl-4 LoF worms were treated with 0.5 mM Retigabine, an FDA-approved AED that targets a voltage-gated potassium channel. This treatment rescued seizure duration of the PKG mutant down to wild-type levels where the wild-type recovered in approximately 37 ± 3.6 s and the Retigabine-treated mutant recovered in approximately 26 ± 4.4 s (oneway ANOVA on ranks, F(3,133) = 50.299, P < 0.001); Dunn, P > 0.05, Fig. 5). This is significantly less than the egl-4 LoF control (134 ± 13.6 s) (Dunn, P < 0.05, Fig. 5).

Fig. 5.

Fig. 5

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Treatment with an FDA-approved antiepileptic drug. N2 and egl-4 LoF were pretreated with an FDA-approved human AED, 0.5 mM Retigabine, which significantly lowered the time to recovery in the egl-4 LoF. Error bars represent ± SEM and n ≥ 20

Discussion

Therapies to control epileptic seizures primarily involve mechanisms that modulate ion channel conformation, thereby decreasing neuronal excitability. We demonstrated that by modulating cGMP-dependent protein kinase (PKG), we can alter electroconvulsive seizure duration in C. elegans. Given these results, we have proposed that the cGMP/PKG pathway is a potential new target for investigating seizure mechanism.

In the worm, egl-4 regulates many important behavioral and developmental processes, such as entry into dauer formation, egg-laying, chemosensory function and synaptic transmission. Previous work has determined that egl-4 LoF is sensitive to the acetylcholinesterase inhibitor, aldicarb, suggesting that egl-4 works to regulate presynaptic neurotransmission (Daniels et al. 2000). While there is ample evidence that egl-4 is a strong LoF mutant with non-functional PKG receptors for cGMP (L’Etoile et al. 2002; Fujiwara et al. 2002), we showed that using 8-bromo-cGMP reduced recovery time back to control levels. This may be due to cGMP directly activating cGMP-gated ion channels (Liu et al. 2010), or the exogenous cGMP could have an effect on transcription factors leading to multiple physiological reactions (Hahm et al. 2009). This further supports our idea that the cGMP/PKG pathway might function in modulating neuronal excitability.

It is interesting to note that the GoF response to ES is not different from the wild-type in several of our results, and we hypothesize this could be due to several different reasons. Interestingly, according to the researchers that characterized the allele, the egl-4 GoF protein levels are significantly reduced as compared to the wild-type worms, which would appear opposite from what is expected (Raizen et al. 2006). The group reported many physiological processes that were opposite of the expected LoF phenotypes and proposed that perhaps there is less stability in protein folding or there is altered subcellular distribution of PKG in the GoF strain (Raizen et al. 2006). Additionally, there have been other studies investigating both GoF and LoF alleles where LoF appears to differ from the wild-type phenotype, unlike the GoF. In one particular study that investigated C. elegans tastant behavior, the egl-4 LoF allele was more sensitive to an aversive tastant, in this case 1 mM quinine, and the egl-4 GoF was not different from wild-type (Krzyzanowski et al. 2013). These findings provide evidence that our results are not out of the ordinary regarding the GoF allele.

Lastly, we have demonstrated that the egl-4 LoF seizure phenotype can be rescued by pretreatment with an FDA-approved AED. Our laboratory has used Retigabine with C. elegans in the past to show that human seizure therapeutics can successfully be used to alter recovery time in invertebrates; however, regarding N2, the drug must be used in conjunction with a chemical convulsant to induce an effect (Opperman et al. 2017; Risley et al. 2016). We hypothesize this is due to the increased seizure threshold for N2. The main target of Retigabine in mammals is a voltage-gated potassium channel, KCNQ2/3 (Barrese et al. 2010; Friedman et al. 2015; Rundfeldt 1997). The C. elegans ortholog of is kqt-1/2/3; therefore, it is possible that this drug works in a similar mechanism. These results and previous results suggest, however, that Retigabine reduces excitability and lessens the time to recovery. Additionally, we found that modulating PKG in vivo alters recovery time from an electroconvulsive seizure. Using genetic and pharmacological manipulation in the ES assay, the data support an unexplored target for seizure exploration.

Acknowledgements

Research was supported by a compound transfer grant (CTP) Grant from Pfizer WI225058 for KD-S. Some strains were provided by the CGC, which is funded by National Institute of Health (NIH) Office of Research Infrastructure Programs (P40 OD010440).

Funding Research was supported by a compound transfer grant (CTP) grant from Pfizer WI225058 for KD-S.

Footnotes

Conflict of interest The authors declare that they have no conflict of interest.

Data availability The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Monica G. Risley and Stephanie P. Kelly co-first authorship.

References

  1. Barrese V, Miceli F, Soldovieri MV, Ambrosino P, Iannotti FA, Cilio MR et al. (2010) Neuronal potassium channel openers in the management of epilepsy: role and potential of retigabine. Clin Pharmacol 2:225–236. 10.2147/cpaa.s15369 [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Brodie MJ, Barry SJ, Bamagous GA, Norrie JD, Kwan P (2012) Patterns of treatment response in newly diagnosed epilepsy. Neurology 78(20):1548–1554. 10.1212/WNL.0b013e3182563b19 [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Calahorro F, Ruiz-Rubio M (2011) Caenorhabditis elegans as an experimental tool for the study of complex neurological diseases: Parkinson’s disease, Alzheimer’s disease and autism spectrum disorder. Invert Neurosci 11(2):73–83. 10.1007/s10158-011-0126-1 [DOI] [PubMed] [Google Scholar]
  4. Caplan SL, Milton SL, Dawson-Scully K (2013) A cGMP-dependent protein kinase (PKG) controls synaptic transmission tolerance to acute oxidative stress at the Drosophila larval neuromuscular junction. J Neurophysiol 109(3):649–658. 10.1152/jn.00784.2011 [DOI] [PubMed] [Google Scholar]
  5. Chalfie M, Tu Y, Euskirchen G, Ward WW, Prasher DC (1994) Green fluorescent protein as a marker for gene expression. Science 263(5148):802–805 [DOI] [PubMed] [Google Scholar]
  6. Daniels SA, Ailion M, Thomas JH, Sengupta P (2000) egl-4 acts through a transforming growth factor-beta/SMAD pathway in Caenorhabditis elegans to regulate multiple neuronal circuits in response to sensory cues. Genetics 156(1):123–141 [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Dawson-Scully K, Bukvic D, Chakaborty-Chatterjee M, Ferreira R, Milton SL, Sokolowski MB (2010) Controlling anoxic tolerance in adult Drosophila via the cGMP-PKG pathway. J Exp Biol 213(Pt 14):2410–2416. 10.1242/jeb.041319 [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Friedman LK, Slomko AM, Wongvravit JP, Naseer Z, Hu S, Wan WY et al. (2015) Efficacy of retigabine on acute limbic seizures in adult rats. J Epilepsy Res 5(2):46–59. https://doi.org/10.14581/jer.15010 [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Fujiwara M, Sengupta P, McIntire SL (2002) Regulation of body size and behavioral state of C. elegans by sensory perception and the EGL-4 cGMP-dependent protein kinase. Neuron 36(6): 1091–1102 [DOI] [PubMed] [Google Scholar]
  10. Guerrini R, Rosati A, Giordano F, Genitori L, Barba C (2013) The medical and surgical treatment of tumoral seizures: current and future perspectives. Epilepsia 54(Suppl 9):84–90. 10.1111/epi.12450 [DOI] [PubMed] [Google Scholar]
  11. Hahm JH, Kim S, Paik YK (2009) Endogenous cGMP regulates adult longevity via the insulin signaling pathway in Caenorhabditis elegans. Aging Cell 8(4):473–483. 10.1111/j.1474-9726.2009.00495.x [DOI] [PubMed] [Google Scholar]
  12. Hamamichi S, Rivas RN, Knight AL, Cao S, Caldwell KA, Caldwell GA (2008) Hypothesis-based RNAi screening identifies neuroprotective genes in a Parkinson’s disease model. Proc Natl Acad Sci USA 105(2):728–733. 10.1073/pnas.0711018105 [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Kaun KR, Hendel T, Gerber B, Sokolowski MB (2007) Natural variation in Drosophila larval reward learning and memory due to a cGMP-dependent protein kinase. Learn Mem 14(5):342–349. 10.1101/lm.505807 [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Kim JB (2014) Channelopathies. Korean J Pediatr 57(1):1–18. 10.3345/kjp.2014.57.1.1 [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Krzyzanowski MC, Brueggemann C, Ezak MJ, Wood JF, Michaels KL, Jackson CA et al. (2013) The C. elegans cGMP-dependent protein kinase EGL-4 regulates nociceptive behavioral sensitivity. PLoS Genet 9(7):e1003619 10.1371/journal.pgen.1003619 [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Lee SK (2014) Old versus new: why do we need new antiepileptic drugs? J Epilepsy Res 4(2):39–44 [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. L’Etoile ND, Coburn CM, Eastham J, Kistler A, Gallegos G, Bargmann CI (2002) The cyclic GMP-dependent protein kinase EGL-4 regulates olfactory adaptation in C. elegans. Neuron 36(6):1079–1089 [DOI] [PubMed] [Google Scholar]
  18. Levitan D, Doyle TG, Brousseau D, Lee MK, Thinakaran G, Slunt HH et al. (1996) Assessment of normal and mutant human presenilin function in Caenorhabditis elegans. Proc Natl Acad Sci USA 93(25):14940–14944 [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Link CD, Taft A, Kapulkin V, Duke K, Kim S, Fei Q et al. (2003) Gene expression analysis in a transgenic Caenorhabditis elegans Alzheimer’s disease model. Neurobiol Aging 24(3):397–413 [DOI] [PubMed] [Google Scholar]
  20. Liu J, Ward A, Gao J, Dong Y, Nishio N, Inada H et al. (2010) C. elegans phototransduction requires a G protein-dependent cGMP pathway and a taste receptor homolog. Nat Neurosci 13(6):715–722. 10.1038/nn.2540 [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Loscher W, Schmidt D (2011) Modern antiepileptic drug development has failed to deliver: ways out of the current dilemma. Epilepsia 52(4):657–678. 10.1111/j.1528-1167.2011.03024.x [DOI] [PubMed] [Google Scholar]
  22. Mary Jane E, Catharyn TL, Andrea MS, Larisa MS (2012) Epilepsy across the spectrum: promoting health and understanding. The National Academies Press, Washington, DC: [PubMed] [Google Scholar]
  23. Mery F, Belay AT, So AK, Sokolowski MB, Kawecki TJ (2007) Natural polymorphism affecting learning and memory in Drosophila. Proc Natl Acad Sci USA 104(32):13051–13055. 10.1073/pnas.0702923104 [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Opperman KJ, Mulcahy B, Giles AC, Risley MG, Birnbaum RL, Tulgren ED et al. (2017) The HECT family ubiquitin ligase EEL-1 regulates neuronal function and development. Cell Rep 19(4):822–835. 10.1016/j.celrep.2017.04.003 [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Raizen DM, Cullison KM, Pack AI, Sundaram MV (2006) A novel gain-of-function mutant of the cyclic GMP-dependent protein kinase egl-4 affects multiple physiological processes in Caenorhabditis elegans. Genetics 173(1):177–187. 10.1534/genetics.106.057380 [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Renger JJ, Yao WD, Sokolowski MB, Wu CF (1999) Neuronal polymorphism among natural alleles of a cGMP-dependent kinase gene, foraging, in Drosophila. J Neurosci 19(19):RC28. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Risley MG, Kelly SP, Jia K, Grill B, Dawson-Scully K (2016) Modulating behavior in. C. elegans using electroshock and antiepileptic drugs. PLoS ONE 11(9):e0163786 10.1371/journal.pone.0163786 [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Rundfeldt C (1997) The new anticonvulsant retigabine (D-23129) acts as an opener of K+ channels in neuronal cells. Eur J Pharmacol 336(2–3):243–249 [DOI] [PubMed] [Google Scholar]
  29. Saeki S, Yamamoto M, Iino Y (2001) Plasticity of chemotaxis revealed by paired presentation of a chemoattractant and starvation in the nematode Caenorhabditis elegans. J Exp Biol 204(Pt 10):1757–1764 [DOI] [PubMed] [Google Scholar]
  30. Szaflarski JP, Nazzal Y, Dreer LE (2014) Post-traumatic epilepsy: current and emerging treatment options. Neuropsychiatr Dis Treat 10:1469–1477. 10.2147/ndt.s50421 [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Timmons L, Court DL, Fire A (2001) Ingestion of bacterially expressed dsRNAs can produce specific and potent genetic interference in Caenorhabditis elegans. Gene 263(1–2):103–112 [DOI] [PubMed] [Google Scholar]
  32. White JG, Southgate E, Thomson JN, Brenner S (1986) The structure of the nervous system of the nematode Caenorhabditis elegans. Philos Trans R Soc Lond B Biol Sci 314(1165):1–340 [DOI] [PubMed] [Google Scholar]
  33. Zhang Y, Lu H, Bargmann CI (2005) Pathogenic bacteria induce aversive olfactory learning in Caenorhabditis elegans. Nature 438(7065):179–184. 10.1038/nature04216 [DOI] [PubMed] [Google Scholar]

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